A process for producing a corresponding unsaturated carboxylic acid or unsaturated nitrile from propylene or isobutylene by gas-phase catalytic oxidation or gas-phase catalytic ammoxidation has heretofore been well known. In recent years, an attention has been given to a process for producing a corresponding unsaturated carboxylic acid or unsaturated nitrile by gas-phase catalytic oxidation or gas-phase catalytic ammoxidation using propane or isobutane instead of propylene or isobutylene.
Various oxide catalysts have been proposed as catalysts for gas-phase catalytic ammoxidation. In general, an oxide obtained by mixing molybdenum, vanadium, and the like, as appropriate, and calcining the mixture is directly used as such a catalyst. Meanwhile, an approach for further post-treatment of the catalyst thus calcined has also been studied for producing the unsaturated carboxylic acid or the unsaturated nitrile.
For example, Patent Document 1 discloses an approach which involves impregnating a Mo—V—Sb/Te catalyst with a solution containing one or more element(s) selected from the group consisting of tungsten, molybdenum, chromium, zirconium, titanium, niobium, tantalum, vanadium, boron, bismuth, tellurium, palladium, cobalt, nickel, iron, phosphorus, silicon, rare earth element, an alkali metal, and alkaline earth metal. Patent Document 2 discloses an approach which involves mixing a catalyst with additives such as an antimony compound, a molybdenum compound, a tellurium compound, and a tungsten compound and subjecting the mixture to reaction, or involves mixing a catalyst or a catalyst precursor with the additives, calcining the mixture, followed by reaction.